2-stroke engines have been used for a variety of mobile and stationary applications. They are advantageous for many applications due to the fact that they have few moving parts, are easy to maintain, and offer a superior weight-to-power ratio.
Conventionally, 2-stroke engines operate by drawing in a mixture of air, fuel and lubricant into the combustion chamber (i.e., the space formed by the top of a piston, the wall of a cylinder in which the piston travels, and a cylinder head that seals off the top end of the cylinder) as the piston approaches the bottom dead center position. This mixture is then compressed by the piston, causing the mixture to reach a pressure at which it can be ignited by an ignition source, such as a spark plug, when the piston is approximately at the top dead center position. The resulting explosion drives the piston downward in what is known as the power stroke. As the piston reaches bottom dead center, exhaust gases exit from the combustion chamber through a port in the cylinder wall or a poppet valve in the cylinder head, and a fresh mixture of air, fuel and lubricant is drawn into the combustion chamber for the next cycle.
Thus, the piston is driven through a power stroke with each revolution of the engine's crankshaft (in contrast to a 4-cycle engine, in which a power stroke occurs every other revolution of the crankshaft).
It is also known to directly inject the fuel into the combustion chamber, provide a separate air flow, and spray oil into the crankcase below the piston, as disclosed in, for example, U.S. Pat. No. 4,579,093 to Eanes.